¶"Vista is bloated" is an understatement
Windows Vista is bloated.
No, I mean, it's bloated. Really bloated. Massively waterlogged needs-immediate-surgery bloated.
My current Windows XP SP2 installation takes 6GB. Of that, about 4GB of it is the fully patched XP installation itself, with the other ~2GB including an installation of Visual Studio 2005 SP1 and some miscellaneous tools such as OpenOffice. Therefore, I figured that devoting 15GB of my 120GB laptop hard drive to a Vista x64 system drive would be more than adequate, given a 2.5x multiplier. I installed Vista x64, ran Windows Update, and let it do its thing, which took a loooong time... only to find out that I was running low on disk space. Yes, I know about the hard links in the Windows folder blah blah blah, but this was an actual popup warning from Explorer itself and the drive did actually have less than 500MB free.
Let me repeat that again: I had a Vista x64 installation, with NO applications installed on it, that was running out of disk space just patching. And we're not even talking about Vista SP1 -- this is pre-SP1 patching. Vista SP1 says requires a minimum of 5GB to install, which is a bit remarkable given that it's a 700MB patch... and filling an NTFS drive to the brim is not a good idea.
I dug around a bit on the C: drive and managed to do a couple of things to free up disk space -- got rid of the hiberfil.sys file, moved the page file onto another partition, nuked all volume shadow copies, etc. In the end, I still only ended up with about 5GB of space free, with over 9GB being taken up in the Windows directory, of which about 5GB is in WinSXS (which is basically the new DLL cesspool). And I still don't have any applications installed. None. Perhaps I should change the boot entry to read Windows Vista Capable, since it's good for nothing.
Now, I conceded a long time ago that having Windows nicely cordoned off in a small little partition on the side, like I used to do in the Windows 95/98 days, doesn't work anymore. There's too much software that forcibly installs on the C: drive to make this work, and as a result I now allocate a beefier system partition and put all of my applications on it as well. Microsoft's current trend of eating gobs of disk space for patching, installing, and general garbage is making this hard, though. I really hate the "one big partition" setup, where all of your data and system files are mixed together, everything fragments like crazy, all of your useful data is three subdirectories down, and you lose everything if the one filesystem dies. Yet Microsoft seems absolutely determined to burn more and more disk space on absurd uses, such as 10% for the Windows Installer baseline cache, 15% for System Restore, and so on. Note that these are percentages, so if you get a bigger disk, they'll just use more by default. And since I work on a video processing application, I kinda need space for other things....
Certain people on the Windows team clearly need to be smacked upside the head with regard to resource usage. Perhaps the Windows team should talk to the Office team, which does a better job of keeping install footprint down and actually lets you skip components during install. It's not just x64, because not everything is duplicated between x86 and x64, and I don't remember XP x64 being this bloated. It wouldn't be so bad except that the amount of disk space being used seems to be outstripping the rate at which I'm getting bigger hard drives. I had a 120GB drive in my Inspiron 9300, and when I configured my current Latitude D830, the biggest hard disk that Dell offered was a 160GB (the 200GB+ drives were only on the Inspiron line, which I passed on for other reasons). With the current trend of leaning back toward more compact and efficient systems, we're actually starting to see devices with less storage space. I was actually considering getting an Asus Eee, which only has anywhere from between 4GB to 24GB of storage, depending on how much you expand/hack/solder to it. Just getting an XP installation to fit is a challenge at that rate, much less Vista.
At the moment, I'm installing Vista SP1 anyway, to see how it fares. The beta SP1 required something like 7GB for x86 and 12GB for x64; the RTM version requires a bit less and seems to be progressing so far. I'm not overly concerned about it blowing up, since all of my important data is still on the old laptop. If it fails, though, I'll probably try using vLite to slipstream SP1 -- I already did that for VS2005 SP1, since it too takes something like 2GB extra if you install it normally, and I could strip more junk that way. Regardless, I refuse to devote something like a quarter of my hard drive to Vista... that's outrageous.